Gob temperature control



June 20 1967 H. L. PENBERTHY GOB TEMPERATURE CONTROL Original Filed Oct.18, 1962 Esca 52.52,@

A TTORNE YS United States Patent ffice 3,326,655 Patented June 20, 19677 Claims. (Cl. 65-l28) The present application is a continuation of mycopending application Ser. No. 231,505 filed Oct. 18, 1962 for GobTemperature Control, now abandoned.

This invention relates to an improved method and apparatus formanufacturing glass and glass products and more particularly relates toan improved forehearth for a glass furnace and a method of operating thesame.

In the operation of glass furnaces and the forehearths thereof,difficulty is frequently encountered in withdrawing the glass from theforehearth in such a manner that the withdrawn glass is of asubstantially uniform temperature. As an example, in the use of a gobfeeder in the manufacture of glass articles, temperature inhomogeneityin the individual gobs can result in non-uniform thickness and strength,and non-uniform optical properties in the finished articles. The problemis well recognized and has been the subject of numerous proposals forsolution. As an example, see United States Patents Nos. 1,680,543,1,928,288, 1,928,289, 1,999,744, 2,919,297, 2,913,509, and BritishPatents Nos. 892,989 and 892,990.

As most prior workers have recognized, the primary problem is created byheat loss through the walls and fioor of the forehearth tending todestroy the temperature homogeneity which at least theoretically existsat the time that the molten glass begins its travel down the forehearth.For the most part, the prior attempts at solving the problem haveinvolved the use of Joule effect electrodes disposed in the forehearthin a position to heat the glass immediately prior to the time that itpasses through the delivery outlet. In certain instances, this isaccomplished by flowing Joule effect currents through the glasshorizontally across the top of the delivery outlet. In more numerouscases, Joule effect currents are flowed from the electrodes in theforehearth in the vicinity of the delivery outlet to a ring typeelectrode substantially at the delivery outlet and completely orsubstantially completely surrounding the glass leaving the deliveryoutlet.

While certain of these proposed solutions have effected a modicum ofimprovement in the situation, nonehas completely eliminated thedifficulty. As an example, while the arrangements utilizing the ringtype electrode have modified the temperature inhomogeneity due to thecooling effect of the forehearth walls, the currents flowing from theelectrodes to the ring have themselves produced heated streaks in theglass issuing from the delivery outlet. This in turn causes thin areasin the perimeters of bottles manufactured according to such a process.In other arrangements where specially shaped electrodes are utilized toapply heat to the discharging glass in a more uniform fashion,difficulties arise in obtaining and maintaining the proper spacing andadjustment of the electrodes during operation.

According to the present invention it has now been found that it ispossible to -provide a temperature homogeneity or uniformity in thedischarged glass of a substantially higher quality than that which canbe practically achieved by any of the prior methods. In the presentinvention temperature uniformity in the glass issuing from the deliveryoutlet of the forehearth is achieved by conditioning the glass in theforehearth prior to the time that it reaches the delivery outlet. Thebasic principle of the invention is that the glass should be held inwhat might be called a heat cocoon in the terminal portion of its travelto the feeder bowl. The glass should be substantially at the desiredorifice temperature at the time that it enters this last zone and theconditioning necessary to compensate for the various heat lossesaccomplished in the heat cocoon. This is to be contrasted with priormethods in which the attempts to secure ternperature homogeneityinvolved Joule effect heating of the glass in the bowl and in someinstances even during its issuance from the orifice.

Thus, the present invention envisions a method and apparatus of feedingglass from a forehearth having an orifice or delivery outlet comprisingthe steps of feeding molten glass into the forehearth at one end,thereafter feeding it into a heat cocoon at substantially the desiredorifice temperature, and withdrawing glass from the orifice whilesimultaneously conditioning the glass in the heat cocoon by subjectingthe surface of the glass to heat from above the surface and creatingJoule effect heat in the glass below the surface, and adjusting the rateof introduction of the above surface heat to the rate of introduction ofthe below surface heat so that the temperature of the glass issuing fromthe orifice is substantially uniform.

It is accordingly a primary object of the present invention to providean improved method and apparatus for manufacturing glass.

It is another object of the invention to provide an improved method andapparatus of feeding molten glass from a forehearth.

It is another object of the invention to provide an improved method andapparatus of heating glass from a forehearth which results in improveduniformity of temperature of the gobs in a double gob operation,irnproved uniformity of temperature around the perimeter of a gob onsingle gob operation, increased forming speeds, reduced tendency todefects in bottles manufactured from the glass, 4better distribution ofthe glass in the finished bottle with resulting higher pressure testsand more uniform optical qualities in the bottles.

It is another object of the invention to provide a meth- 0d andapparatus of feeding glass from a forehearth having a bowl with adelivery outlet, comprising the steps of feeding molten glass into theforehearth at one end, thereafter feeding the glass int-o a conditioningzone at an average temperature substantially the same as the desireddelivery outlet temperature, withdrawing glass from the delivery outletat the other end, and conditioning the glass in the conditioning znebefore it reaches the bowl by subjecting the glass to heat both fromabove and below its surface so that the glass issuing from the deliveryoutlet is of substantially uniform temperature.

It is another object of the invention to provide an apparatus forproducing glass including a forehearth connected at one end to a furnaceand having a delivery outlet with first and second heating meansarranged between the point of connection of the forehearth to thefurnace and the delivery outlet, one of such heating means being abovethe surface level of the glass while the other is below the surfacelevel of the glass, with the rate of introduction of the heat from thefirst and second heating means being so adjusted that the temperature ofglass issuing from the delivery outlet is substantially uniform.

It is another object of the invention to provide an improved method andapparatus for feeding molten glass from a forehearth wherein asubstantial uniformity of temperature across the cross section of a gobis achieved by subjecting the glass to a conditioning in the region ofthe forehearth immediately upstream of the bowl, and adjusting the4ratio of sub-surface heating to above-surface heating in that region.

These and further objects and advantages of the invention will becomemore apparent upon reference to the following specification and claimsand the appended drawings wherein:

FIGURE 1 is a horizontal section of a forehearth constructed accordingto the present invention; and

FIGURE 2 is a vertical section of the forehearth yof FIGURE 1 takenapproximately along the line 22 of FIGURE 1.

Referring more particularly to the figures of the drawing, there isindicated generally at a forehearth in the conventional form of a troughhaving an inner lining of refractory material which resists the actionof glass and heat. The trough is connected to the `working zone 12 of asuitable glass furnace and comprises a lioor 14, roof 16 and opposedside walls 18. Referring to FIGURE l, the width of the forehearth isnecked down at 20 to termlnate in the conventional bowl 22 having an endwall 24. The bowl 22 has a delivery outlet or orifice 26 at its bottomfrom which the molten glass issues. A suitable shearing device 28 may beprovided to form gobs of glass 30 in a conventional manner.

A first heating means is provided in the forehearth in the form ofadjustable gas burners or electric heating elements 32 which aredisposed along the length of the forehearth and which subject thesurface 36 of the molten glass 34 to above surface heat. An adjustablepower source 37 is connected in conventional fashion to heating elements32 to control the quantity of heat provided, as will be understood byone skilled in the art.V A second means for feeding heat into the glassin the forehearth is provided in the form of a series of Joule effectelectrodes 38, 40 and 42, disposed at the floor of the forehearth, whichare connected to one or more suitable power sources shown in FIGURE 2 asadjustable power source 43 so as to create Joule effect currents throughthe glass in the forehearth. I

The method of operation according to the inventlon comprises utilizationof the portion of the forehearth immediately preceding the bowl anddelivery outlet as a conditioning zone or heat cocoon which places theglass in such a condition that after it issues from the delivery outletit is at a substantially uniform temperature. This zone is indicated atA in FIGURE 2. Thus, the glass is heated by the electrodes 38, 40 and 42to compensate for the heat losses from the side walls and floor of theforehearth and is heated by the above surface heat source 32 tocompensate for the heat losses through the superstructure of theforehearth in that section. According to the invention, the glassentering his special condition-v ing section of the forehearth has anaverage temperature which is substantially the same as the desiredtemperature of the final gob, so that the average temperature of theglass in this conditioning section is neither being raised nor lowered.This permits the glass to even out its own temperature differences byradiation and cionduction.

In the conventional forehearth the glass enters the forehearth at atemperature higher than the desired gobl temperature and therefore somecooling is necessary before the glass arrives at the orifice. Accordingto the present invention this cooling, where necessary, is accomplishedin the section of the forehearth upstream of the conditioning zone A,or, as is indicated in FIGURE 2, in the zone B. However, while this isnormally a cooling zone, it is desirable to provide above surface heatand sometimes sub-surface heat in order to control the rate of coolingof the glass to insure that it enters conditioning zone A at an averagetemperature which is substantially the same as the desired orificetemperature. This apparatus and mode of operation is to be clearlydistinguished from certain prior procedures, such as disclosed in U.S.Patents Nos. 1,928,288 and 1,928,289, wherein the forehearth is providedwith an initial cooling zone that drops the temperature of the glassbelow the temperature desired in the charge.

A further feature of the invention is the desirability of substantiallyeliminating J oule effect heating in the bowl. The reason for this is asfollows: When electric current ows between two electrodes in a glassmass there is always a preferred current path between the electrodesdependent primarily upon the local temperature conditions in the glass.In a forehearth the glass temperatures are relatively low and the slopeof the resistance-temperature curve is steep. The initial current iioWthrough the preferred path heats the glass therein thereby lowering itsresistance and making the path an even more preferred one. This resultsin a hot streak of glass and when it exists in the bowl it almost alwaysproduces a hot streak ofV glass in the gob. As a result, the preferredembodiment of the present invention comprehends a substantial absence ofJoule effect heating in the bowl. As a practical matter very smallamounts of Joule effect heating may be tolerated in the bowl but thismust be only a very small fraction of the amount which occurs in theconditioning zon-e A. As an example, 10 watts of Joule effect heating inthe bowl would produce no ill effects, while l0 kilowatts would bedisastrous to the results desired. The amount which can be toleratedwill depend upon the geometry and operating conditions of theinstallation. As stated, the preferred embodiment of the inventioncomprehends a substantial elimination of Joule effect heating in thebowl.

The iiow of glass through a forehearth is complex and is not preciselyunderstood because of the difliculty of investigation. However, certainphenomena have been ascertained. In a conventional fuel red forehearththere are four main sources of thermal inhomogeneity in the gobs: (l)The temperature gradient downward through the glass caused by heatlosses through the bottom of the channel which are made up by the fuelfire over the top of the glass; (2) The sharp temperature gradient (skineffect) in the thin layer of glass immediately adjacent a cooledrefractory wall. This layer flows slowly toward the orifice; (3) Thechanneling effect which occurs because the hotter glass tends to owthrough the central portion of the channel, further aggravatingtemperature differences due to bottom heat loss; and (4) the cycling oftemperature following gob-weight adjustments. When the gob Weight isincreased, glass flows faster along the channel, and soon the glassarriving at the orifice is hotter because it has had less time to cool.Hotter glass at the orilice means heavier gobs, and the operator mustadjust the feeder to reduce the gob weight. The cycle then goes in areverse direction, and so on.

It is of the essence of the present invention that the undesired effectsof these varied causes of thermal inhomogeneity are combatted en mass bydelivering the glass to the heat cocoon of conditioning zone A atsubstantially the desired orifice temperature, and then adjusting theratio of sub-surface heat to above surface heat in zone A empiricallyto` bring about a uniformity of temperature around the circumference ofthe gobs as measured,'for example, by an optical pyrometer shown at 50in FIGURE 2. Optical pyrometer 50 may be of any commercially availabletype such as that sold under the name Pyro by the Pyrometer InstrumentCompany, Inc., of Bergeneld, NJ. Other means of observing the desiredoperating conditions may be resorted to. Thus, thermocouples may beinstalled in the conditioning zone A to measure glass temperatures atthe surface of the glass and at the fioor of the forehearth.Observations may then be made to correlate these readings with thedesired gob temperatures and control may thereafter be predicated on thethermocouple readings. The end result in either method is the same,i.e., the temperature around the periphery of the gobs is maintained ata uniform level. The simpler method is that of measuring the temperatureof the gob surface around its perimeter with an optical pyrometer andthen adjusting the heat ratio to equalize the perimeter temperature tothe maximum extent possible. With such an arrangement, it is found thatthe temperature difference around the perimeter of the gobs can be heldequal within the accuracy of measurement of the pyrometer. This hasproven to be a highly satisfactory method of control susceptible of easyadjustment and maintenance.

When utilizing the method and apparatus of the invention, it has beenfound possible to achieve a substantial uniformity of temperature in theoutput of the forehearth with the following benefits: (l) More evendistribution of the glass in the sidewalls of containers beingmanufactured with a concomitant increase in pressure test. As anexample, the industry average pressure test for a yrepresentative sampleof cone-top stubby beer bottles was 150 p.s.i. On the other hand bottlesfrom an installation of the forehearth of this invention tested 190-200p.s.i.; (2) Less trouble with checks on the finish; (3) Easier doublegob mold operation. With double gob amber glass operation, it has beenobserved that the temperatures from one side of one gob to the otherside of the other gob can be different by as much as 20 F. In such acase the mold will probably be too cold for one gob and too hot for theother. With the method and apparatus of this invention the gobtemperatures are equal and the moldgob temperature relationship is thesame for both gobs; (4) Machine speeds can be increased. As an example,in one installation of the method and apparatus of the invention, speedwas increased from 76 to 82 bottles per minute, with a small increase inpercentage pack; and (5) Closer control of gob weight.

The invention may be embodied in other specific forms without departingfrom the spirit or essential characteristics thereof. The presentembodiment is therefore to be considered in all respects as illustrativeand not restrictive, the scope of the invention being indicated by theappended claims rather than by the foregoing description, and allchanges which come within the meaning and range of equivalency of theclaims are therefore intended to be embraced therein.

What is claimed and desired to be secured by United States lettersPatent is:

1. A forehearth having an upstream end connected to a furnace and havinga bowl and delivery orifice at the downstream end, said forehearthconstituting a trough having therein a substantially uniform depth ofmolten glass from said upstream end to said bowl, heating means in afirst zone immediately upstream of' said bowl for subjecting said moltenglass in said first zone to above surface heat and to low levelsub-surface Joule effect heat, heating means in a second zone in saidforehearth immediately upstream of said first zone for controlling theaverage temperature of the glass flowing to said first zone so that theaverage temperature of the glass flowing from said second zone to saidfirst zone is substantially the same as the temperature of the glassissuing from said orifice, means for determining the temperature of theglass issuing from said orifice, and means for adjusting the intensityof heat created by said heating means in said first zone and the rati-oof above surface to sub-surface heat in said first Zone so that glasspassing through such first zone remains at substantially the sameaverage temperature and so that glass issuing from said orifice is ofsubstantially uniform temperature as indicated by said means fordetermining temperatu-re.

2. A forehearth as set out in claim 1 wherein said means for creatingsub-surface Joule effect heat comprises Joule effect electrodes enteringsaid forehearth immediately upstream of said bowl.

3, A forehearth as set out in claim 2 wherein the Joule effectelectrodes in said forehearth are so arranged that substantially noJoule effect heating occurs in said bowl.

4. A forehearth as set out in claim 1 wherein said trough is ofsubstantially uniform width from said upstream portion to said bowl.

5. A method of feeding glass from a forehearth having an upstreamportion into which glass is delivered from a furnace and a downstreambowl with an orifice from which glass is withdrawn, the molten glass insaid forehearth having substantially uniform depth from said upstreamportion to said bowl, comprising the st-eps of determining thetemperature of the glass issuing from the orifice, subjecting the glassin a region immediately upstream of said bowl to above surface heat andto subsurface Joule effect heat, conditioning the glass immediatelyupstream of said region so that its average temperature as `it reachessaid -region is substantially the same as the temperature of the glassissuing from said orifice, and adjusting the rate of subjection of saidabove surface and subsurface heat and the ratio of said above surfaceand sub1-surface heat so that the glass passing through said regionremains at the same average temperature and the glass issuing from saidorifice remains at the same average temperature.

6. A method as set out in claim S including the step of confining thedownstream excursion of said Joule effect heat substantially to saidregion so that substantially no Joule effect heating occurs in saidbowl.

7. A forehearth as set out in claim 1 wherein the heating means in saidfirst zone includes above-surface heaters and Joule effect electrodesdisposed below the surface of the molten glass and wherein saidadjusting means comprises separate adjustable power sources individuallyconnected to the Joule effect electrodes, and to the above-surfaceheaters.

References Cited UNITED STATES PATENTS 1,944,855 l/l934 Wadman -347 X3,133,803 5/1964 Denman 65-134 DONALL H. SYLVESTER, Primary Examiner. A.D. KELLOGG, Assistant Examiner.

1. A FOREHEARTH HAVING AN UPSTREAM END CONNECTED TO A FURNACE AND HAVINGA BOWL AND DELIVERY ORIFICE AT THE DOWNSTREAM END, SAID FOREHEARTHCONSTITUTING A TROUGH HAVING THEREIN A SUBSTANTIALLY UNIFORM DEPTH OFMOLTEN GLASS FROM SAID UPSTREAMS END TO SAID BOWL, HEATING MEANS IN AFIRST ZONE UMMEDIATELY UPSTREAM OF SAID BOWL FOR SUBJECTING SAID MOLTENGLASS IN SAID FIRST ZONE TO ABOVE SURFACE HEAT AND TO LOW LEVELSUB-SURFACE JOULE EFFECT HEAT, HEATING MEANS IN A SECOND ZONE IN SAIDFOREHEARTH IMMEDIATELY UPSTREAM OF SAID FIRST ZONE FOR CONTROLLING THEAVERAGE TEMPERATURE OF THE GLASS FLOWING TO SAID FIRST ZONE SO THAT THEAVERAGE TEMPERATURE OF THE GLASS FLOWING FROM SAID SECOND ZONE TO SAIDFIRST ZONE IS SUBSTANTIALLY THE SAME AS THE TEMPERATURE OF THE GLASSISSUING FROM SAID ORIFICE, MEANS FOR DETERMINING THE TEMPERATURE OF THEGLASS ISSUING FROM SAID ORIFICE, AND MEANS FOR ADJUSTING THE INTENSITYOF HEAT CREATED BY SAID HEATING MEANS IN SAID FIRST ZONE AND THE RATIOOF ABOVE SURFACE TO SUB-SURFACE HEAT IN SAID FIRST ZONE SO THAT GLASSPASSING THROUGH SUCH FIRST ZONE REMAINS AT SUBSTANTIALLY THE SAMEAVERAGE TEMPERATURE AND SO THAT GLASS ISSUING FROM SAID ORIFICE IS OFSUBSTANTIALLY UNIFORM TEMPERATURE AS INDICATED BY SAID MEANS FORDETERMINING TEMPERATURE.
 5. A METHOD OF FEEDING GLASS FROM A FOREHEARTHHAVING AN UPSTREAM PORTION INTO WHICH GLASS IS DELIVERED FROM A FURNACEAND A DOWNSTREAM BOWL WITH ANORIFICE FROM WHICH GLASS IS WITHDRAWN, THEMOLTEN GLASS IN SAID FOREHEARTH HAVING SUBSTANTIALLY UNIFORM DEPTH FROMSAID UPSTREAM PORTION TO SAID BOWL, COMPRISING THE STEPS OF DETERMINGTHE TEMPERATURE OF THE GLASS ISSUING FROM THE ORIFICE, SUBJECTING THEGLASS IN A REGION IMMEDIATELY UPSTREAM OF SAID BOWL TO ABOVE SURFACEHEAT AND TO SUBSURFACE JOULE EFFECT HEAT, CONDITIONING THE GLASSIMMEDIATGELY UPSTREAM OF SAID REGION SO THAT ITS AVERAGE TEMPERATURE ASIT REACHES SAID REGION IS SUBSTANTIALLY THE SAME AS THE TEMPERATURE OFTHE GLASS ISSUING FROM SID ORIFICE, AND ADJUSTING THE RATE OF SUBJECTIONOF SAID ABVE SURFACE AND SUB-SURFACE HEAT AND THE RATIO OF SAID ABOVESURFACE AND SUB-SURFACE HEAT SO THAT THE GLASS PASSING THROUGH SAIDREGION REMAINS AT THE SAME AVERAGE TEMPERATURE AND THE GLASS ISSUINGFROM SAID ORIFICE REMAINS AT THE SAME AVERAGE TEMPERATURE.